Multiple zone heater

ABSTRACT

A multi-zone heater with a plurality of thermocouples such that different heater zones can be monitored for temperature independently. The independent thermocouples may have their leads routed out from the shaft of the heater in a channel that is closed with a joining process that results in hermetic seal adapted to withstand both the interior atmosphere of the shaft and the process chemicals in the process chamber. The thermocouple and its leads may be enclosed with a joining process in which a channel cover is brazed to the heater plate with aluminum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/831,670, to Elliot et al., filed Mar. 15, 2013, which claims priorityto U.S. Provisional Application No. 61/658,896 to Elliot et al., filedJun. 12, 2012, which is hereby incorporated by reference in itsentirety, and which claims priority to U.S. Provisional Application No.61/707,865 to Elliot et al., filed Sep. 28, 2012, which is herebyincorporated by reference in its entirety, and which claims priority toU.S. Provisional Application No. 61/728,810 to Elliot et al., filed Nov.21, 2012, which is hereby incorporated by reference in its entirety, andwhich claims priority to U.S. Provisional Application No. 61/757,090 toElliot et al., filed Jan. 25, 2013, which is hereby incorporated byreference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to heater used in semiconductorprocessing, and more specifically to a heater with multiple heater zonesand thermocouples to monitor those zones.

Description of Related Art

In semiconductor manufacturing, silicon substrates (wafers) areprocessed at elevated temperatures for deposition of numerous differentmaterials. Temperatures typically range in the 300-550 C range, but canat times go as high as 750 C or even higher. The deposited materials are“grown” in a layer on the surface of the wafer. Many of these materialshave growth rates which are extremely sensitive to temperature, sovariations of the temperature across the wafer can affect the localgrowth rate of the film, causing variations in the film thickness as itis grown across the wafer.

It is desired to control the variations in thickness of the depositedfilms. Sometimes it is desired to have the films thicker in the centerof the wafer (like a dome). Sometimes it is desired to have the filmsthicker on the edge (like a crater or dimple). Sometimes it is desiredto have the film thickness as even as possible (within tens ofangstroms).

One of the most direct methods for controlling the temperature of thewafer, and thereby the thickness profile of the as-deposited films, isto place the wafer on a heater. By designing the heater with a specificwatt-density “map” which produces the temperature profile desired on thewafer, the desired film thickness profile can be produced. Watt-densityof the underlying heater is increased in the location(s) where highertemperatures are desired on the wafer, and decreased in the location(s)where lower wafer temperatures are desired.

It is desired by chip manufacturers to have the ability to run differentprocesses in the same process chamber. Capital equipment for growingfilms is very expensive (more than $1 million per process chamber istypical), so it is desired to maximize the usage of, and minimize thenumber of required process chambers. Different temperature processeswith different chemistries are run in the same chamber to producedifferent films. These different films may also have differentgrowth-rate vs. temperature behavior. This leads the chip manufacturersto desire the ability to change the watt-density map of a heater in agiven process chamber “on-the-fly” to achieve the desired film thicknessprofile.

Additionally, it is desired by chip manufacturers to have the ability torun exactly the same “recipe” in multiple process chambers and producefilms that have matching film thickness profiles (as well as otherproperties which can be affected by temperature such as film stress,refractive index, and others). Therefore, it is desired to have theability to produce a heater which can have very repeatable watt-densitymaps from unit to unit.

A heater can be made with the ability to change the watt-density map byusing multiple independent heater circuits within the heater. By varyingthe voltages and currents applied to the different circuits, you canchange the power levels in the locations of the individual circuits. Thelocations of these specific circuits are called “zones”. By increasingthe voltage (and thereby the current as these heater elements are allresistance heaters) to a given zone, you increase the temperature inthat zone. Conversely, when you decrease the voltage to a zone, youdecrease the temperature in that zone. In this way, differentwatt-density maps can be produced by the same heater by changing thepower to the individual zones.

At least two limitations have affected chip makers' ability toeffectively use multi-zone heaters. The first limitation is that currentstate-of-the-art heaters have only one control thermocouple. Only onecontrol thermocouple can be used because the plate-and-shaft designcurrently used for heaters allows for location of a thermocouple at thecenter of the heater plate only, or within a radius of ˜1 inch of thecenter of the heater. Thermocouples are made of metals which areincompatible with the processing environment of the wafer, and thereforemust be isolated from that environment. Additionally, for fastestresponse of a thermocouple (TC) it is best to have it operating in anatmospheric pressure environment, not the vacuum environment of atypical process chamber. Therefore, TCs can only be located within thecentral hollow area of the heater shaft which is not in communicationwith the process environment. If there are heater zones located outsideof the 2 inch diameter of the heater shaft, then no TC can be installedthere to monitor and help control the temperature of that zone.

This limitation has been addressed by using “slaved” power ratios tocontrol heater zones located outside of the central area of the heater.Ratios are established of the power to be applied to the central zoneand to each of the other zones which produce the desired watt-densitymap. The central control TC monitors the temperature of the centralzone, and the power applied to the central zone (which is based on thefeedback of the central control TC) is then applied to all zones asadjusted by the pre-established ratios. For example, with a two-zoneheater, let us assume that a ratio of 1.2 to 1.0 of power applied to theouter and inner zones produces the desired temperature profile. Let usassume that the heater control system, by reading the temperature dataprovided by the central control TC, determines that a voltage of 100 VACis needed to achieve the proper temperature. With the slaved ratiocontrol methodology, a voltage of 120 VAC will thereby be applied to theouter heater zone, and a voltage of 100 VAC will be applied to the innerzone. The watt-density map can thereby be adjusted by changing the slaveratios.

This leads us to the second limitation. Current state-of-the-art heatershave an inherent variation of the resistance of the embedded heater(s).Due to the high temperatures and pressures required in the manufacturingprocess of current ceramic heaters, the resistance tolerance achievablecan approach 50%. In other words, a typical resistance for asemiconductor-grade ceramic heater element is within a range of 1.8-3.0ohms (at room temperature—the heater element material is typicallymolybdenum, which increases in resistance as the operating temperatureincreases).

This variation causes a problem with maintaining a repeatablewatt-density-map from unit to unit with multi-zone heaters controlled bythe slave-ratio method. With single zone heaters, the resistancevariation may not be an issue, because a control TC is utilized tomonitor the actual operating temperature, and power levels fed to theheater are adjusted accordingly. But if you have a multi-zone heater,and the heater element resistance variations can approach 50%, then theslave ratio control methodology will not produce a repeatable wattdensity map from unit to unit.

What is called for is to establish a heater design which will allowinstallation of multiple control TCs which can be physically locatedwithin the respective heater zones to allow for feedback and controldirectly, and yet still keep the TCs isolated from the processingenvironment within the process chamber.

SUMMARY OF THE INVENTION

A multi-zone heater with a plurality of thermocouples such thatdifferent heater zones can be monitored for temperature independently.The independent thermocouples may have their leads routed out from theshaft of the heater in a channel that is closed with a joining processthat results in hermetic seal adapted to withstand both the interioratmosphere of the shaft and the process chemicals in the processchamber. The independent thermocouples may have their leads routed outfrom the shaft of the heater in a space between plate layers, whereinthe plate layers are joined with a joining process that results inhermetic seal adapted to withstand both the interior atmosphere of theshaft and the process chemicals in the process chamber. The thermocoupleand its leads may be enclosed with a joining process in which a channelcover, or a bottom plate layer, is brazed to the heater plate withaluminum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a plate and shaft device used in semiconductorprocessing according to some embodiments of the present invention.

FIG. 2 is a cross-sectional view of a joint between a plate and shaftaccording to some embodiments of the present invention.

FIG. 3 is a view of a plate and shaft device in a process chamberaccording to some embodiments of the present invention.

FIG. 4 is a view of a heater device according to some embodiments of thepresent invention.

FIG. 5 is an illustrative cross-sectional sketch of a multi-zone heateraccording to some embodiments of the present invention.

FIG. 6 is an illustrative bottom view of a multi-zone heater accordingto some embodiments of the present invention.

FIG. 7 is an illustrative view of a joined cover plate according to someembodiments of the present invention.

FIG. 8 is an illustrative view of a cover plate according to someembodiments of the present invention.

FIG. 9 is a perspective view of a heater according to some embodimentsof the present invention.

FIG. 10 is a perspective exploded view of a heater according to someembodiments of the present invention.

FIG. 11 is an illustrative cross-sectional view of a heater with amulti-layer plate according to some embodiments of the presentinvention.

FIG. 12 is a close up partial cross-sectional view of a multi-layerplate according to some embodiments of the present invention.

FIG. 13 is an illustrative cross-sectional view of a heater withmultiple heater zones and thermocouples according to some embodiments ofthe present invention.

FIG. 14 is a close-up cross-sectional view of plate and shaft joint areaaccording to some embodiments of the present invention.

FIG. 15 is a top view of a central hub according to some embodiments ofthe present invention.

FIG. 16 is a partial cross-sectional view illustrating aspects of acentral hub according to some embodiment of the present invention.

FIG. 17 is a mapping illustration of multiple heater zones according tosome embodiments of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary plate and shaft device 100, such as aheater, used in semiconductor processing. In some aspects, the plate andshaft device 100 is composed of a ceramic, such as aluminum nitride. Theheater has a shaft 101 which in turn supports a plate 102. The plate 102has a top surface 103. The shaft 101 may be a hollow cylinder. The plate102 may be a flat disc. Other subcomponents may be present. In somepresent processes, the plate 102 may be manufactured individually in aninitial process involving a process oven wherein the ceramic plate isformed. In some embodiments, the plate may be joined to the shaft with alow temperature hermetic joining process as described below.

FIG. 2 shows a cross section in which a first ceramic object, which maybe a ceramic shaft 191, for example, may be joined to a second ceramicobject, which may be made of the same or a different material, and whichmay be a ceramic plate 192, for example. A joining material, such asbrazing layer 190, may be included, which can be selected from thecombinations of braze layer materials described herein and may bedelivered to the joint according to the methods described herein. Insome aspects, the plate may be aluminum nitride and the shaft may bealuminum nitride, zirconia, alumina, or other ceramic. In some aspects,it may be desired to use a shaft material with a lower conductivethermal transfer coefficient in some embodiments.

With respect to the joint depicted in FIG. 2, the shaft 191 may bepositioned such that it abuts the plate, with only the brazing layerinterposed between the surfaces to be joined, for example surface 193 ofthe shaft and surface 194 of the plate. The interface surface 194 of theplate 192 may reside in a recess 195 in the plate. The thickness of thejoint is exaggerated for clarity of illustration. In an exemplaryembodiment, the plate and shaft may both be of aluminum nitride and bothhave been separately formed previously using a liquid phase sinteringprocess. The plate may be approximately 9-13 inches in diameter and 0.5to 0.75 inches thick in some embodiments. The shaft may be a hollowcylinder which is 5-10 inches long with a wall thickness in the 0.1inches and an exterior diameter in the range 1-3 inches. The plate mayhave a recess adapted to receive an outer surface of a first end of theshaft.

As seen in FIG. 3, the brazing material of joints used on heaters, orother devices, may bridge between two distinct atmospheres, both ofwhich may present significant problems for prior brazing materials. Onan external surface 207 of the semiconductor processing equipment, suchas a heater 205, the brazing material must be compatible with theprocesses occurring in, and the environment 201 present in, thesemiconductor processing chamber 200 in which the heater 205 will beused. The environment 201 present in the processing chamber 200 mayinclude fluorine chemistries. The heater 205 may have a substrate 206affixed to a top surface of the plate 203, which is supported by a shaft204. On an internal surface 208 of the heater 205, the brazing layermaterial must be compatible with a different atmosphere 202, which maybe an oxygenated atmosphere. Prior brazing materials used with ceramicshave not been able to meet both of these criteria. For example, brazeelements containing copper, silver, or gold may interfere with thelattice structure of the silicon wafer being processed, and are thus notappropriate. However, in the case of a brazed joint joining a heaterplate to a heater shaft, the interior of the shaft typically sees a hightemperature, and has an oxygenated atmosphere within the center of a thehollow shaft. The portion of the braze joint which would be exposed tothis atmosphere will oxidize, and may oxidize into the joint, resultingin a failure of the hermeticity of the joint. In addition to structuralattachment, the joint between the shaft and the plate of these devicesto be used in semiconductor manufacturing must be hermetic in many, ifnot most or all, uses.

FIG. 4 shows one embodiment of a schematic illustration of a heatercolumn used in a semiconductor processing chamber. The heater 300, whichmay be a ceramic heater, can include a radio frequency antenna 310, aheater element 320, a shaft 330, a plate 340, and a mounting flange 350.

In some embodiments of the present invention, as seen in FIG. 5, a coverplate 501 may be bonded to the backside of a heater plate 502, coveringa hollow area 503 that may be contiguous with the heater shaft hollowcore 504. The use of a radial feeder, such as the covered hollow area,allows individual control thermocouples to be used to directly monitorthe local temperature at each heater zone of a multi-zone heater.Thermocouples 505, 506, 507 may be installed within thermocouple wells508, 509, 510 located at each individual heater zone. The thermocouplesmay be installed into these wells which are located within the coveredhollow area, or channel. In some embodiments, machining of the plate maybe performed in the channel to allow for deeper installation of thethermocouple. The thermocouples may then be covered with a ceramic coverplate 501 positioned on the heater plate backside and between the heaterplate and shaft. The heater plate, hollow area cover plate, and heatershaft are then bonded together. This isolates the thermocouples from theprocess environment, and provides direct feedback of the temperature ofeach heater zone for traditional control. In some heater designs, theheater is fully embedded within the plate during the manufacturingprocess of the plate. This processing may entail high temperature, whichmay be in the range of 1700 C, and high pressing contact force duringthe formation of the plate. Although the heater element itself may beadapted to withstand this processing, thermocouples and the leads intothe thermocouples, which may be made of Inconel, are not able towithstand this processing. With installation of thermocouples after thefinal sintering and pressing of the ceramic plate, the thermocouplesmust then be protected from the process chemistries which the heaterwill be exposed to during its use. The use of multiple thermocouples tomonitor the temperature of areas of the plate which have separateheaters allows for temperature control of these areas of the plate basedupon actual temperature readings.

The thermocouple wells may reach into the plate to the level of theheater element. In some embodiments, the heater element may have an openarea so that the thermocouple well does not go down into the heaterelement, but to the same depth in an area where there is a gap or spacein the heater element. In some embodiments, the hollow area, and thethermocouple wells, may be machined into the heater plate afterfabrication of the heater plate with the multi-zone heater elementswithin it. The multi-zone heater elements may be in the ceramic heaterplate when the plate is manufactured. The hollow area cover plate may bejoined to the heater plate, and in some aspects also to a portion of theshaft, using a low temperature joining process as described herein.

FIG. 6 is a bottom view illustration of a plate with a shaft attachedthereto, with a hollow channel area seen extending radially outward fromthe portion of the plate which resides within the center of the hollowshaft. Within this hollow channel area there may be a one or morethermocouple wells which allow for the insertion of thermocouples toheater element zones which could not otherwise be directly monitored.

FIG. 7 illustrates a cross-sectional view of a heater plate 502 with ahollow area 503 and cover plate 501 according to some embodiments of thepresent invention. The cover plate 501 may be adapted to fit within aslot in the bottom of the heater plate. Below the slot, a channel 503may be present adapted to route electrical coupling 520 from thethermocouples to the shaft center. The joints 521 attaching the coverplate 501 to the heater plate 502 bridge different atmospheres, as thechannel may see the atmosphere within the center of the shaft, whichlikely will be oxygenated. This atmosphere within the channel may allowfor significantly better thermocouple function for a thermocouple withinthe channel area. The other side of the joint will see the atmospherewithin the process chamber, which may include corrosive process gasses,such as fluorine chemistries. An appropriate joining method results in ajoint compatible with these various atmospheres.

FIG. 8 illustrates a cross-sectional view of a heater plate with ahollow cover 530 plate adapted to be joined to the bottom of a heaterplate 502. The hollow cover plate 530 may cover thermocouple couplingwires 520 as well as thermocouple wells in the bottom of the heaterplate. In such embodiments, the channel is within the cover plate asopposed to the main heater plate structure.

FIGS. 9 and 10 illustrate, in perspective and partially explodedperspective views, respectively, a heater 540 according to someembodiment of the present invention. The hollow cover plate 541 may havea contiguous ring feature adapted to reside between the shaft 542 andthe bottom of the heater plate 543. The hollow cover plate 541 allowsfor the routing of thermocouple wires from the bottom of the plate,outside of the perimeter of the shaft, to the center of the shaft. Theheater plate 543, hollow cover plate 541, and shaft 542 may besimultaneously joined in a single heating operation which brazes thecomponents together in some embodiments.

In some embodiments of the present invention, as seen in expanded viewin FIG. 11, a plate and shaft device 500 is seen with a plate assembly501 and a shaft 502. The plate assembly 501 has layers 503, 504, 505which are fully fired ceramic layers prior to their assembly into theplate assembly 501. The top plate layer 503 overlays the middle layer504 with an electrode layer 506 residing between the top plate layer 503and the middle layer 504. The middle layer 504 overlays the bottom layer505 with a heater layer 507 residing between the middle layer 504 andthe bottom layer 505.

In some embodiments, thermocouples may be mounted in between platelayers in order to monitor temperatures at different locations. Amulti-layer plate assembly may allow for access to areas on one or moresurfaces of one or more of the plates such that machining of surfacesmay be done after the final firing of a ceramic plate layer. Further,this access to surfaces may also allow for the assembly of componentsinto the surfaces of the plate layers, and into the spaces between theplate layers.

The layers 503, 504, 505 of the plate assembly 501 may be of a ceramicsuch as aluminum nitride in the case of a heater, or other materialsincluding alumina, doped alumina, AlN, doped AlN, beryllia, dopedberyllia and others in the case of an electrostatic chuck. The layers503, 504, 505 of the plate assembly that makes up the substrate supportmay have been fully fired ceramic prior to their introduction into theplate assembly 501. For example, the layers 503, 504, 505 may have beenfully fired as plates in a high temperature high contact pressurespecialty oven, or tape cast, or spark-plasma sintered, or other method,and then machined to final dimension as required by their use and theirposition in the stack of the plate assembly. The plate layers 503, 504,505 may then be joined together using a brazing process with joininglayers 508 which allow the final assembly of the plate assembly 501 tobe done without the need for a specialty high temperature oven equippedwith a press for high contact stresses.

In embodiments wherein a shaft is also part of the final assembly, suchas in the case of a plate and shaft device, the plate assembly 501 toshaft 502 joining process step may also use a brazing process donewithout the need for a specialty high temperature oven equipped with apress for high contact stresses. The joining of the plate layers, andthe plate assembly to the shaft, may be done in a simultaneous processstep in some embodiments. The shaft 502 may be joined to the plateassembly 501 with a joining layer 509. The joining layer 509 may be abrazing element which is identical to the joining layers 508 in someembodiments.

An improved method for manufacturing a plate, or plate assembly, mayinvolve the joining of layers of the plate assembly, which have beendescribed above and are described in more detail below, into a finalplate assembly without the time consuming and expensive step of anadditional processing with high temperatures and high contact pressures.The plate layers may be joined with a brazing method for joiningceramics according to embodiments of the present invention. An exampleof a brazing method for joining together first and second ceramicobjects may include the steps of bringing the first and second objectstogether with a brazing layer selected from the group consisting ofaluminum and an aluminum alloy disposed between the first and secondceramic objects, heating the brazing layer to a temperature of at least800 C, and cooling the brazing layer to a temperature below its meltingpoint so that the brazing layer hardens and creates a hermetic seal soas to join the first member to the second member. Various geometries ofbraze joints may be implemented according to methods described herein.

In some embodiments of the present invention a plate assembly withlayers may be presented such that standoffs are present between thelayers of the plate such that when the joining layer is heated, andslight pressure is applied axially to the plates, there is slight axialcompression such that the joining layer is mildly thinned until thestandoff on one plate contacts the adjacent plate. In some aspects, thisallows for not just control of the joint thickness but also fordimensional and tolerance control of the plate assembly. For example,the parallelism of features of the various plates can be set by machinetolerances on the plate layers, and this aspect can be maintained duringthe joining process with the use of standoffs. In some embodiments,post-joining dimensional control may be achieved using a circumferentialouter ring on one plate layer which overlays an inner ring on anadjacent layer to provide axial conformance. In some embodiments, one ofthe outer ring or the inner ring may also contact the adjacent plate inan axial direction perpendicular to the plate such that positionalcontrol is also achieved in that axial direction. The axial positionalcontrol may also thus determine the final thickness of a joining layerbetween the two adjacent plates.

In some embodiments of the present invention an electrode between layersmay be of the same material as the joining layer, and may function in adual capacity of both the joining layer and the electrode. For example,the area previously occupied by an electrode in an electrostatic chuckmay instead be occupied by a joining layer which has the dual functionof performing as an electrode, for providing electrostatic clampingforce for example, and of performing as a joining layer to join the twoplates between which the joining layer resides. In such embodiments, alabyrinth may be around the periphery of the two joined plate such thatline of sight, and access in general, to the charged electrode from aregion outside of the plate is minimized.

FIG. 12 illustrates a partial cross-section of a plate assemblyaccording to some embodiments of the present invention. The plateassembly is a multi-layer plate assembly with both a heater and anelectrode residing between different layers. The layers are joined withbrazing elements and the final position of the plates in a directionperpendicular to the plane of the primary plane of the plates isdictated by standoffs 568, 569 on the plates.

A top plate layer 561 overlays a lower plate layer 562. The lower platelayer 562 overlays a bottom plate layer 563. Although illustrated inFIG. 12 with three plate layers, different numbers of plate layers maybe used according to the needs of a particular application. The topplate layer 561 is joined to the lower plate layer 562 using amulti-function joining layer 566. The multi-function joining layer 566is adapted to provide joining of the top plate layer 561 to the lowerplate layer 562 and to be an electrode. Such an electrode may be ajoining layer that is substantially a circular disc, wherein the joiningmaterial also functions as an electrode. As seen in FIG. 12, a standoff568 is adapted to provide positional control of the top plate layer 561to the lower plate layer 562 in a vertical direction perpendicular tothe primary plane of the plate layers. The rim of the top plate layer561 is adapted to remove line of sight along the boundary 567 betweenthe two plates at their periphery. The thickness of the joining layer566 may be sized such that the joining layer 566 is in contact with thetop plate layer 561 and the lower plate layer 562 prior to the step ofheating and joining the plate assembly.

The lower plate layer 562 overlays the bottom plate layer 563. A heater564 resides between the lower plate layer 562 and the bottom plate layer563. A joining layer 565 joins the lower plate layer 562 to the bottomplate layer 563. The joining layer 565 may be an annular ring within theperiphery of the plate layers. A standoff 569 is adapted to providepositional control of the lower plate layer 562 to the bottom platelayer 563 in a vertical direction perpendicular to the primary plane ofthe plate layers. During a joining step of the plate assembly, thecomponents as seen in FIG. 12 may be pre-assembled, and then this platepre-assembly may be joined using processes described herein to form acompleted plate assembly. In some embodiments, this plate pre-assemblymay be further preassembled with a shaft and shaft joining layer suchthat a complete plate and shaft device may be joined in a single heatingprocess. This single heating process may not require a high temperatureoven, or a high temperature oven with presses adapted to provide highcontact stresses. In addition, in some embodiments the completed plateand shaft assembly may not require any post-joining machining yet maystill meet the tolerance requirements of such a device in actual use insemiconductor manufacturing.

In some embodiments, the top plate layer and the bottom plate layer arealuminum nitride. In some embodiments the joining layer is aluminum.Examples of the joining process and materials are discussed below.

FIG. 13 is an illustrative cross-sectional view of a heater 600 withmultiple heater zones and multiple thermocouples using a multi-layerplate 601 according to some embodiments of the present invention. Inthese embodiments, the use of a hermetic joining layer, also adapted towithstand corrosive processing chemistries, allows for the insertion ofthermocouples into the portion 605 of the plate outside of the areacircumscribed by the interior 603 of the shaft 602, yet protected fromthe corrosive process gasses to which the heater may be subjected.

In some embodiments, the use of a multi-layer plate allows for access toa space between layers in which thermocouples can be placed into regionsotherwise not able to be monitored. For example, in a plate and shaftdevice 600 such as seen in FIG. 13, all power and monitoring aretypically routed through the hollow center 603 of the shaft 602, and outof the processing chamber via a chamber feedthrough. In prior artdevices wherein the entire ceramic plate and shaft device was hotsintered together, the only available area in which to embed athermocouple, and route the telemetry down the hollow shaft, was in thearea within the center of the hollow shaft. For example, a hole could bedrilled in the bottom of the plate using a long drill adapted to go downthe center of the hollow shaft. A thermocouple could then be insertedinto that hole, and be used to monitor the temperature of the plate inthat central region only. This limitation on the location of where athermocouple could be mounted precluded the monitoring of temperaturesat locations which fell outside of the interior of the hollow shaft.

In some embodiments, a central hub 604 may be used to help facilitatethe sealing of the inter-layer space between plate layers from theatmosphere which may be present within the shaft. In such embodiments,the central hub 604 may act as a feed through from the central portionof the shaft and the inter-layer space between plate layers.

The plate 601 of the heater 600 may be assembled from three plate layersin some embodiments. Each of the plate layers may be of a fully firedceramic such as aluminum nitride. Each of the plate layers may bepreviously machined to a final, or near final, dimension prior to beingassembled into the multi-layer plate assembly. A top plate layer 612 mayoverlay a middle plate layer 611, which may in turn overlay a bottomplate layer 610. The middle plate layer may be joined around itsperiphery to the bottom plate layer 610 with a joining layer 610. Ametal layer 613 between the top plate layer 612 and the middle platelayer 611 may function as an RF layer, and as the joining layer betweenthe plate layers. There may be one or more heater elements between themiddle plate layer 611 and the lower plate layer 610. The middle platelayer 611 may be adapted to receive the heater elements such that theheater elements 621 reside in grooves in the bottom of the middle platelayer 611. An example of a multi-zone heater element layout is seen inFIG. 17. The heater element is split into three radial zones, each ofwhich have two halves, for a total of six elements. Two of the radialzones are fully outside 605 the periphery of the interior of the hollowshaft. Thus, thermocouples located in those zones adapted to providetemperature monitoring would be placed into the plate at a radialdistance greater than the shaft interior radius. The heater elements 621may be of molybdenum, and may be potted into the grooves with an AlNpotting compound 622. Power leads for the heater elements may splay outfrom the central hub to route power to the individual heater circuits.

In embodiments such as seen in FIGS. 13-16, the bottom surface of themiddle plate layer 611 may see installation of a variety of components.In some aspects, grooves may be machined into this surface for theinstallation of heater elements. Holes may be drilled into this surfaceto act as thermocouples wells for installation of thermocouples. Afterthis machining, the heater elements may be installed and potted. In someembodiments, the heater elements may be molybdenum wires placed in thegrooves. In some embodiments, the heater elements may be deposited intothe grooves using a thick film deposition technique. The thermocouplesmay be installed and potted as well. The heater elements may be attachedto the power leads, which may be bus bars. In embodiments wherein acentral hub is used, power leads and thermocouple leads may be routedthrough the central hub. The multi-layer plate stack may be assembled,such as in an upside down fashion, wherein all elements, including brazelayers, are assembled into a pre-assembly which would then be processedinto a final, complete, heater assembly. A brazing step according todescriptions herein would join all of the components with a hermeticseal adapted to withstand the atmospheres that the heater would seewhile supporting semiconductor manufacturing, which may includeoxygenated atmospheres, and fluorine chemistries.

With the routing of leads through the central hub 604, such as athermocouple lead with an Inconel exterior, these leads may be routedthrough the central hub and also sealed with a brazing element. Forexample, a lead may be routed through a hole in the central hub whichhad a counterbore, and a cylindrical brazing element may be placedaround the lead prior to the brazing step. The central hub 604 alsoallows the inter-plate space between the middle plate layer and thebottom plate layer to be hermetically sealed from the interior space ofthe shaft. As seen in FIG. 14, a joining layer 615 may be used to sealthe shaft from the bottom of the bottom plate layer, and another joininglayer 616 may be used to seal the central hub 604 from the upper surfaceof the bottom plate layer. In some embodiments, when the entire heaterassembly is heated in vacuum during the brazing step to join all of thevarious surfaces that are to be attached by the various joining layers,the inter plate spaces will be sealed in a vacuum condition withhermetic seals. In some aspects, having the inter plate space whereinthe thermocouples are mounted will better thermally isolate thethermocouples from temperatures seen in areas other than where they aremounted.

FIGS. 15 and 16 illustrate the central hub 604 in top and partialcross-sectional views, respectively. The central hub may be used as ahermetic feedthrough which isolates the central area of the shaft fromthe inter plate space between the middle plate layer and the bottomplate layer. The leads which supply power to the heaters, and thethermocouple leads, may be routed through the central hub and sealedwith the brazing material in the same brazing process step which joinsand seals the other components to each other.

FIG. 17 illustrates a multi-zone heater element as seen in someembodiments of the present invention. The heater element is split intothree radial zones, each of which have two halves, for a total of sixelements. Two of the radial zones are fully outside 605 the periphery ofthe interior of the hollow shaft.

Joining methods according to some embodiments of the present inventionrely on control of wetting and flow of the joining material relative tothe ceramic pieces to be joined. In some embodiments, the absence ofoxygen during the joining process allows for proper wetting withoutreactions which change the materials in the joint area. With properwetting and flow of the joining material, a hermetically sealed jointcan be attained at relatively low temperature. In some embodiments ofthe present invention, a pre-metallization of the ceramic in the area ofthe joint is done prior to the joining process.

In some applications where end products of joined ceramics are used,strength of the joint may not be the key design factor. In someapplications, hermeticity of the joint may be required to allow forseparation of atmospheres on either side of the joint. Also, thecomposition of the joining material may be important such that it isresistant to chemicals which the ceramic assembly end product may beexposed to. The joining material may need to be resistant to thechemicals, which otherwise might cause degeneration of the joint, andloss of the hermetic seal. The joining material may also need to be of atype of material which does not negatively interfere with the processeslater supported by the finished ceramic device.

In some embodiments of the present invention, the joined ceramicassembly is composed of a ceramic, such as aluminum nitride. Othermaterials, such as alumina, silicon nitride, silicon carbide orberyllium oxide, may be used. In some aspects, a first ceramic piece maybe aluminum nitride and a second ceramic piece may be aluminum nitride,zirconia, alumina, or other ceramic. In some present processes, thejoined ceramic assembly components may first be manufacturedindividually in an initial process involving a process oven wherein thefirst piece 72 and the second piece 71 are formed. In some embodiments,a recess may be included in one of the mating pieces, which allows theother mating piece to reside within the recess.

In some embodiments, the joint may include a plurality of standoffsadapted to maintain a minimum braze layer thickness. In someembodiments, one of the ceramic pieces, such as the shaft, may utilize aplurality of standoffs mesas on the end of the shaft which is to bejoined to the plate, or on the surface where the cover is to be joinedto the plate, for example. The mesas may be part of the same structureas the ceramic piece, and may be formed by machining away structure fromthe piece, leaving the mesas. The mesas may abut the end of the ceramicpiece after the joining process. In some embodiments, the mesas may beused to create a minimum braze layer thickness for the joint. In someembodiments, the braze layer material, prior to brazing, will be thickerthan the distance maintained by the mesas or powder particles betweenthe shaft end and the plate. In some embodiments, other methods may beused to establish a minimum braze layer thickness. In some embodiments,ceramic spheres may be used to establish a minimum braze layerthickness. In some aspects, the joint thickness may be slightly thickerthan the dimension of the standoffs, or other minimum thicknessdetermining device, as not quite all of the braze material may besqueezed out from between the standoffs and the adjacent interfacesurface. In some aspects, some of the aluminum braze layer may be foundbetween the standoff and the adjacent interface surface. In someembodiments, the brazing material may be 0.006 inches thick prior tobrazing with a completed joint minimum thickness of 0.004 inches. Thebrazing material may be aluminum with 0.4 Wt. % Fe. In some embodiments,standoffs are not used.

A braze material which will be compatible with both of the types ofatmospheres described above when they are seen on both sides across ajoint in such a device is aluminum. Aluminum has a property of forming aself-limiting layer of oxidized aluminum. This layer is generallyhomogenous, and, once formed, prevents or significantly limitsadditional oxygen or other oxidizing chemistries (such a fluorinechemistries) penetrating to the base aluminum and continuing theoxidation process. In this way, there is an initial brief period ofoxidation or corrosion of the aluminum, which is then substantiallystopped or slowed by the oxide (or fluoride) layer which has been formedon the surface of the aluminum. The braze material may be in the form ofa sheet, a powder, a thin film, or be of any other form factor suitablefor the brazing processes described herein. For example, the brazinglayer may be a sheet having a thickness ranging from 0.00019 inches to0.011 inches or more. In some embodiments, the braze material may be asheet having a thickness of approximately 0.0012 inches. In someembodiments, the braze material may be a sheet having a thickness ofapproximately 0.006 inches. Typically, alloying constituents (such asmagnesium, for example) in aluminum are formed as precipitates inbetween the grain boundaries of the aluminum. While they can reduce theoxidation resistance of the aluminum bonding layer, typically theseprecipitates do not form contiguous pathways through the aluminum, andthereby do not allow penetration of the oxidizing agents through thefull aluminum layer, and thus leaving intact the self-limitingoxide-layer characteristic of aluminum which provides its corrosionresistance. In the embodiments of using an aluminum alloy which containsconstituents which can form precipitates, process parameters, includingcooling protocols, would be adapted to minimize the precipitates in thegrain boundary. For example, in one embodiment, the braze material maybe aluminum having a purity of at least 99.5%. In some embodiments, acommercially available aluminum foil, which may have a purity of greaterthan 92%, may be used. In some embodiments, alloys are used. Thesealloys may include Al-5 w % Zr, Al-5 w % Ti, commercial alloys #7005,#5083, and #7075. These alloys may be used with a joining temperature of1100 C in some embodiments. These alloys may be used with a temperaturebetween 800 C and 1200 C in some embodiments. These alloys may be usedwith a lower or higher temperature in some embodiments.

The non-susceptibility of AlN to diffusion with aluminum under theconditions of processes according to embodiments of the presentinvention results in the preservation of the material properties, andthe material identity, of the ceramic after the brazing step in themanufacturing of the plate and shaft assembly.

In some embodiments, the joining process is performed in a processchamber adapted to provide very low pressures. Joining processesaccording to embodiments of the present invention may require an absenceof oxygen in order to achieve a hermetically sealed joint. In someembodiments, the process is performed at a pressure lower than 1×10E-4Torr. In some embodiments, the process is performed at a pressure lowerthan 1×10E-5 Torr. In some embodiments, further oxygen removal isachieved with the placement of zirconium or titanium in the processchamber. For example, a zirconium inner chamber may be placed around thepieces which are to be joined.

In some embodiments, atmospheres other than vacuum may be used toachieve a hermetic seal. In some embodiments, argon (Ar) atmosphere maybe used to achieve hermetic joints. In some embodiments, other noblegasses are used to achieve hermetic joints. In some embodiments,hydrogen (H2) atmosphere may be used to achieve hermetic joints.

The wetting and flow of the brazing layer may be sensitive to a varietyof factors. The factors of concern include the braze materialcomposition, the ceramic composition, the chemical makeup of theatmosphere in the process chamber, especially the level of oxygen in thechamber during the joining process, the temperature, the time attemperature, the thickness of the braze material, the surfacecharacteristics of the material to be joined, the geometry of the piecesto be joined, the physical pressure applied across the joint during thejoining process, and/or the joint gap maintained during the joiningprocess.

In some embodiments, the surfaces of the ceramic may undergo ametallization prior to the placement of the ceramic pieces into achamber for joining. The metallization may be a frictional metallizationin some embodiments. The frictional metallization may comprise the useof an aluminum rod. A rotary tool may be used to spin the aluminum rodover areas which will be adjacent to the brazing layer when the piece isjoined. The frictional metallization step may leave some aluminum in thesurface of the ceramic piece. The frictional metallization step mayalter the ceramic surface somewhat, such as by removing some oxides,such that the surface is better adapted for wetting of the brazingmaterial. The metallization step may be a thin film sputtering in someembodiments.

An example of a brazing method for joining together first and secondceramic objects may include the steps of bringing the first and secondobjects together with a brazing layer selected from the group consistingof aluminum and an aluminum alloy disposed between the first and secondceramic objects, heating the brazing layer to a temperature of at least800 C, and cooling the brazing layer to a temperature below its meltingpoint so that the brazing layer hardens and creates a hermetic seal soas to join the first member to the second member. Various geometries ofbraze joints may be implemented according to methods described herein.

A joining process according to some embodiments of the present inventionmay comprise some or all of the following steps. Two or more ceramicpieces are selected for joining. In some embodiments, a plurality ofpieces may be joined using a plurality of joining layers in the same setof process steps, but for the sake of clarity of discussion two ceramicpieces joined with a single joining layer will be discussed herein. Theceramic pieces may be of aluminum nitride. The ceramic pieces may be ofmono-crystalline or poly-crystalline aluminum nitride. Portions of eachpiece have been identified as the area of each piece which will bejoined to the other. In an illustrative example, a portion of the bottomof a ceramic plate structure will be joined to the top of a ceramichollow cylindrical structure. The joining material may be a brazinglayer comprising aluminum. In some embodiments, the brazing layer may bea commercially available aluminum foil of >99% aluminum content. Thebrazing layer may consist of a plurality of layers of foil in someembodiments.

In some embodiments, the specific surface areas which will be joinedwill undergo a pre-metallization step. This pre-metallization step maybe achieved in a variety of ways. In one method, a frictionalpre-metallization process is employed, using a rod of material, whichmay be 6061 aluminum alloy, may be spun with a rotary tool and pressedagainst the ceramic in the joint area, such that some aluminum may bedeposited onto each of the two ceramic pieces in the area of the joint.In another method, PVD, CVD, electro-plating, plasma spray, or othermethods may be used to apply the pre-metallization.

Prior to joining, the two pieces may be fixtured relative to each otherto maintain some positional control while in the process chamber. Thefixturing may also aid in the application of an externally applied loadto create contact pressure between the two pieces, and across the joint,during the application of temperature. A weight may be placed on top ofthe fixture pieces such that contact pressure in applied across thejoint. The weight may be proportioned to the area of the brazing layer.In some embodiments, the contact pressure applied across the joint maybe in the range of approximately 2-500 psi onto the joint contact areas.In some embodiments the contact pressure may be in the range of 2-40psi. In some embodiments, minimal pressure may be used. The contactpressure used at this step is significantly lower than that seen in thejoining step using hot pressing/sintering as seen in prior processes,which may use pressures in the range of 2000-3000 psi.

In embodiments using mesas as standoffs, or using other methods of jointthickness control such as ceramic spheres, the original thickness of thebrazing layer prior to the application of heat may be larger than theheight of the mesas. As the brazing layer temperature reaches andexceeds the liquidus temperature, pressure across the brazing layerbetween the pieces being joined will cause relative motion between thepieces until the mesas on a first piece contact an interface surface ona second piece. At that point, contact pressure across the joint will nolonger be supplied by the external force (except as resistance torepulsive forces within the brazing layer, if any). The mesas mayprevent the brazing layer from being forced out of the joint area priorto the full wetting of ceramic pieces, and may thus allow better and/orfull wetting during the joining process. In some embodiments, mesas arenot used.

The fixtured assembly may be placed in a process oven. The oven may beevacuated to a pressure of less than 5×10E-5 Torr. In some aspects,vacuum removes the residual oxygen. In some embodiments, a vacuum oflower than 1×10E-5 Torr is used. In some embodiments, the fixturedassembly is placed within a zirconium inner chamber which acts as anoxygen attractant, further reducing the residual oxygen which might havefound its way towards the joint during processing. In some embodiments,the process oven is purged and re-filled with pure, dehydrated purenoble gas, such as argon gas, to remove the oxygen. In some embodiments,the process oven is purged and re-filled with purified hydrogen toremove the oxygen.

The fixture assembly is then subjected to increases in temperature, anda hold at the joining temperature. Upon initiating the heating cycle,the temperature may be raised slowly, for example 15C per minute to 200C and then 20 C per minute thereafter, to standardized temperatures, forexample, 600 C and the joining temperature, and held at each temperaturefor a fixed dwell time to allow the vacuum to recover after heating, inorder to minimize gradients and/or for other reasons. When the brazetemperature has been reached, the temperature can be held for a time toeffect the braze reaction. In an exemplary embodiment, the dwelltemperature may be 800 C and the dwell time may be 2 hours. In anotherexemplary embodiment, the dwell temperature may be 1000 C and the dwelltime may be 15 minutes. In another exemplary embodiment, the dwelltemperature may be 1150 and the dwell time may be 30-45 minutes. In someembodiments, the dwell temperature does not exceed a maximum of 1200 C.In some embodiments, the dwell temperature does not exceed a maximum of1300 C. Upon achieving sufficient braze dwell time, the furnace may becooled at a rate of 20 C per minute, or lower when the inherent furnacecooling rate is less, to room temperature. The furnace may be brought toatmospheric pressure, opened and the brazed assembly may be removed forinspection, characterization and/or evaluation.

The use of too high of a temperature, for too long of a time period, maylead to voids forming in the joining layer as the result of significantaluminum evaporation. As voids form in the joining layer, thehermeticity of the joint may be lost. The process temperature and thetime duration of the process temperature may be controlled such that thealuminum layer does not evaporate away, and so that a hermetic joint isachieved. With proper temperature and process time duration control, inaddition to the other process parameters described above, a continuousjoint may be formed. A continuous joint achieved in accord withembodiments as described herein will result in a hermetic sealing of theparts, as well as a structural attachment.

The brazing material will flow and allow for wetting of the surfaces ofthe ceramic materials being joined. When ceramic such as aluminumnitride is joined using aluminum brazing layers and in the presence ofsufficiently low levels of oxygen and described herein, the joint is ahermetic brazed joint. This stands in contrast to the diffusion bondingseen in some prior ceramic joining processes.

In some embodiments, the pieces to be joined may be configured such thatno pressure is placed across the brazing layer during brazing. Forexample, a post or shaft may be placed into a countersunk hole or recessin a mating piece. The countersink may be larger than the exteriordimension of the post or shaft. This may create an area around the postor shaft which then may be filled with aluminum, or an aluminum alloy.In this scenario, pressure placed between the two pieces in order tohold them during joining may not result in any pressure across the brazelayer. Also, it may be possible to hold each piece in the preferred endposition using fixturing such that little or no pressure is placedbetween the pieces at all.

Joined assemblies joined as described above result in pieces withhermetic sealing between the joined pieces. Such assemblies are thenable to be used where atmosphere isolation is an important aspect in theuse of the assemblies. Further, the portion of the joint which may beexposed to various atmospheres when the joined assemblies are later usedin semi-conductor processing, for example, will not degrade in suchatmospheres, nor will it contaminate the later semi-conductorprocessing.

Both hermetic and non-hermetic joints may join pieces strongly, in thatsignificant force is needed to separate the pieces. However, the factthat a joint is strong is not determinative of whether the jointprovides a hermetic seal. The ability to obtain hermetic joints may berelated to the wetting of the joint. Wetting describes the ability ortendency of a liquid to spread over the surface of another material. Ifthere is insufficient wetting in a brazed joint, there will be areaswhere there is no bonding. If there is enough non-wetted area, then gasmay pass through the joint, causing a leak. Wetting may be affected bythe pressure across the joint at different stages in the melting of thebrazing material. The use of mesa standoffs, or other standoff devicesuch as the insertion of ceramic spheres or powder particles ofappropriate diameter, to limit the compression of the brazing layerbeyond a certain minimum distance may enhance the wetting of the areasof the joint. Careful control of the atmosphere seen by the brazingelement during the joining process may enhance the wetting of the areasof the joint. In combination, careful control of the joint thickness,and careful control of the atmosphere used during the process, mayresult in a complete wetting of the joint interface area that is notable to be achieved with other processes. Further, the use of a brazinglayer that is of a proper thickness, which may be thicker than the mesastandoff height, in conjunction with the other referenced factors, mayresult in a very well wetted, hermetic, joint. Although a variety ofjoining layer thicknesses may be successful, an increased thickness ofthe joining layer may enhance the success rate of the joint's hermeticaspect.

The presence of a significant amount of oxygen or nitrogen during thebrazing process may create reactions which interfere with full wettingof the joint interface area, which in turn may result in a joint that isnot hermetic. Without full wetting, non-wetted areas are introduced intothe final joint, in the joint interface area. When sufficient contiguousnon-wetted areas are introduced, the hermeticity of the joint is lost.

The presence of nitrogen may lead to the nitrogen reacting with themolten aluminum to form aluminum nitride, and this reaction formationmay interfere with the wetting of the joint interface area. Similarly,the presence of oxygen may lead to the oxygen reacting with the moltenaluminum to form aluminum oxide, and this reaction formation mayinterfere with the wetting of the joint interface area. Using a vacuumatmosphere of pressure lower than 5×10-5 Torr has been shown to haveremoved enough oxygen and nitrogen to allow for fully robust wetting ofthe joint interface area, and hermetic joints. In some embodiments, useof higher pressures, including atmospheric pressure, but usingnon-oxidizing gasses such as hydrogen or pure noble gasses such asargon, for example, in the process chamber during the brazing step hasalso led to robust wetting of the joint interface area, and hermeticjoints. In order to avoid the oxygen reaction referred to above, theamount of oxygen in the process chamber during the brazing process mustbe low enough such that the full wetting of the joint interface area isnot adversely affected. In order to avoid the nitrogen reaction referredto above, the amount of nitrogen present in the process chamber duringthe brazing process must be low enough such that the full wetting ofjoint interface area is not adversely affected.

The selection of the proper atmosphere during the brazing process,coupled with maintaining a minimum joint thickness, may allow for thefull wetting of the joint. Conversely, the selection of an improperatmosphere may lead to poor wetting, voids, and lead to a non-hermeticjoint. The appropriate combination of controlled atmosphere andcontrolled joint thickness along with proper material selection andtemperature during brazing allows for the joining of materials withhermetic joints.

In some embodiments of the present invention wherein one or both of theceramic surfaces is pre-metallized prior to brazing, such as withaluminum thin film sputtering, the joining process steps may use a lowertemperature held for shorter duration. Upon initiating the heatingcycle, the temperature may be raised slowly, for example 15C per minuteto 200 C and then 20 C per minute thereafter, to standardizedtemperatures, for example, 600 C and the joining temperature, and heldat each temperature for a fixed dwell time to allow the vacuum torecover after heating, in order to minimize gradients and/or for otherreasons. When the braze temperature has been reached, the temperaturecan be held for a time to effect the braze reaction. In some embodimentsusing a pre-metallization of one or more of the interface surfaces, thebrazing temperature may be in the range of 600 C to 850 C. In anexemplary embodiment, the dwell temperature may be 700 C and the dwelltime may be 1 minute. In another exemplary embodiment, the dwelltemperature may be 750 C and the dwell time may be 1 minute. Uponachieving sufficient braze dwell time, the furnace may be cooled at arate of 20 C per minute, or lower when the inherent furnace cooling rateis less, to room temperature. The furnace may be brought to atmosphericpressure, opened and the brazed assembly may be removed for inspection,characterization and/or evaluation.

Relative to aluminum brazing processes without a layer of aluminumdeposited onto the joint interface areas, processes wherein the ceramichas had a thin layer of aluminum deposited thereon, such as with a thinfilm sputtering technique, yield hermetic joints at low temperatures andwith very short dwell times at the braze temperature. The use of adeposited layer of aluminum on the interface surface may make thewetting of the surface comparatively easier, and needing less energy,allowing for the use of lower temperatures and shortened dwell times toachieve a hermetic joint.

A process summary for such a brazing process is seen as follows: Thejoint was between two pieces of poly-crystalline aluminum nitride. Thebrazing layer material was of 0.003″ thickness of 99.8% aluminum foil.The joint interface area of the ring piece was metallized using a thinfilm deposition of 2 microns of aluminum. The joining temperature was780 C held for 10 minutes. The joining was done in a process chamberheld at pressure lower than 6×10E-5 Torr. The joint thickness wasmaintained using 0.004″ diameter ZrO2 spheres. The first piece (ring)piece underwent an etching process prior to the deposition of the thinlayer of aluminum. Acoustic imaging of the joint integrity showed asolid dark color in locations where there was good wetting onto theceramic. Good and sufficient integrity of the joint was seen. This jointwas hermetic. Hermeticity was verified by having a vacuum leak rate of<1×10E-9 sccm He/sec; as verified by a standard commercially availablemass spectrometer helium leak detector.

The manufacture of a multi-zone heater assembly, with thermocouplemonitoring of the zones of the heater, according to embodiments of thepresent invention, allows for insertion of thermocouples after the finalfiring of the ceramic pieces of the heater. The thermocouples are alsoprotected from the exterior environment to which the heater will besubjected during semiconductor processing, which may include corrosivegasses, by a hermetic seal adapted to withstand significant temperaturesand those corrosive gasses. In addition, the hermetic seals are also thestructural joints, and the multi-component assemblies may bestructurally connected, and hermetically sealed, with a single brazingstep.

Another advantage of the joining method as described herein is thatjoints made according to some embodiments of the present invention mayallow for the disassembly of components, if desired, to repair orreplace one of those two components. Because the joining process did notmodify the ceramic pieces by diffusion of a joining layer into theceramic, the ceramic pieces are thus able to be re-used.

In some embodiments, alignment and location of the shaft and plate ismaintained by part geometries, eliminating fixturing and post-bondmachining. Weighting may be used to insure there is no movement duringbonding process, other than some axial movement as the braze materialmelts. The plate may be placed top down with a joining element within arecess in the back surface of the plate. The shaft may be insertedvertically downward into the recess within the plate. A weight may beplaced on the shaft 401 to provide some contact pressure during thejoining process.

In some embodiments, location and perpendicularity of shaft/plate ismaintained by fixturing. Fixturing may not be precise due to thermalexpansion and machining tolerances—therefore, post-bond machining may berequired. The shaft diameter may be increased to accommodate requiredmaterial removal to meet final dimensional requirements. Again,weighting may be used to insure there is no movement during bondingprocess, other than some axial movement as the braze material melts. Theplate may be placed top down with a joining element above the backsurface of the plate. The shaft may be placed onto the plate to create aplate and shaft pre-assembly. A fixture is adapted to support and locatethe shaft. The fixture may be keyed to the plate to provide positionalintegrity. A weight may be placed on the shaft to provide some contactpressure during the joining process.

An aspect of the current invention is the maximum operating temperatureof the bonded shaft-plate as defined by the decreasing tensile strength,with temperature, of the aluminum or aluminum alloy selected for thejoining. For example, if pure aluminum is employed as the joiningmaterial, the structural strength of the bond between the shaft andplate becomes quite low as the temperature of the joint approaches themelting temperature of the aluminum, generally considered to be 660 C.In practice, when using 99.5% or purer aluminum, the shaft-plateassembly will withstand all normal and expected stresses encountered ina typical wafer processing tool to a temperature of 600 C. However, somesemiconductor device fabrication processes require temperatures greaterthan 600 C.

A repair procedure for the unjoining of an assembly which has beenjoined according to embodiments of the present invention may proceed asfollows. The assembly may be placed in a process oven using a fixtureadapted to provide a tensile force across the joint. The fixturing mayput a tensile stress of approximately 2-30 psi onto the joint contactarea. The fixturing may put a larger stress across the joint in someembodiments. The fixtured assembly may then be placed in a process oven.The oven may be evacuated, although it may not be required during thesesteps. The temperature may be raised slowly, for example 15C per minuteto 200 C and then 20 C per minute thereafter, to standardizedtemperatures, for example 400C, and then to a disjoining temperature.Upon reaching the disjoining temperature, the pieces may come apart fromeach other. The disjoining temperature may be specific to the materialused in the brazing layer. The disjoining temperature may be in therange of 600-800 C in some embodiments. The disjoining temperature maybe in the range of 800-1000 C in some embodiments. The fixturing may beadapted to allow for a limited amount of motion between the two piecessuch that pieces are not damaged upon separation. The disjoiningtemperature may be material specific. The disjoining temperature may bein the range of 450 C to 660 C for aluminum.

Prior to the re-use of a previously used piece, such as a ceramic shaft,the piece may be prepared for re-use by machining the joint area suchthat irregular surfaces are removed. In some embodiments, it may bedesired that all of the residual brazing material be removed such thatthe total amount of brazing material in the joint is controlled when thepiece is joined to a new mating part.

In contrast to joining methods which create diffusion layers within theceramic, joining processes according to some embodiments of the presentinvention do not result in such a diffusion layer. Thus, the ceramic andthe brazing material retain the same material properties after thebrazing step that they had prior to the brazing step. Thus, should apiece be desired to be re-used after disjoining, the same material andthe same material properties will be present in the piece, allowing forre-use with known composition and properties.

As evident from the above description, a wide variety of embodiments maybe configured from the description given herein and additionaladvantages and modifications will readily occur to those skilled in theart. The invention in its broader aspects is, therefore, not limited tothe specific details and illustrative examples shown and described.Accordingly, departures from such details may be made without departingfrom the spirit or scope of the applicant's general invention.

What is claimed is:
 1. A multi-zone heater, said multi-zone heatercomprising: a multi-layer heater plate, said multi-layer heater platecomprising: a heater plate radial center; a top plate layer, said topplate layer comprising ceramic; one or more intermediate plate layers,said one or more intermediate plate layers comprising ceramic; a bottomplate layer, said bottom plate layer comprising ceramic; a plurality ofplate joining layers disposed between said plate layers, wherein saidjoining layers join said plate layers with hermetic joints; a pluralityof heater element zones between two of the plate layers, said heaterelement zones adapted to be individually controlled; a plurality ofthermocouples, said thermocouples mounted between two of said platelayers and located at a plurality of distances from said heater plateradial center, said thermocouples comprising thermocouple leads; and aceramic hollow heater shaft, said ceramic hollow heater shaftcomprising: an interior surface, said interior surface of said hollowheater shaft defining an interior of said hollow heater shaft; and anexterior surface, wherein said ceramic hollow heater shaft is attachedto a bottom surface of said multi-layer heater plate; wherein each ofthe hermetic joints have a vacuum leak rate of <1×10⁻⁹ sccm He/sec andwherein said thermocouple leads are routed through the interior of saidceramic hollow heater shaft.
 2. The multi-zone heater according to claim1, wherein one or more of said thermocouples are located outside of thearea circumscribed by the exterior surface of said hollow heater shaft.3. The multi-zone heater according to claim 2 further comprising ajoining layer between said hollow heater shaft and said multi-layerplate.
 4. The multi-zone heater according to claim 3, wherein saidplurality of plate joining layers comprise metallic aluminum.
 5. Themulti-zone heater according to claim 4, wherein said joining layerbetween said hollow heater shaft and said multi-layer plate comprisesmetallic aluminum.
 6. The multi-zone heater according to claim 5,wherein said hollow heater shaft comprises aluminum nitride.
 7. Themulti-zone heater according to claim 6, wherein said plurality of platejoining layers comprise metallic aluminum.
 8. The multi-zone heateraccording to claim 7, wherein said joining layer between said hollowheater shaft and said multi-layer plate comprises metallic aluminum. 9.The multi-zone heater according to claim 8 further comprising a centralhub disposed between said hollow heater shaft and said multi-layerplate.
 10. The multi-zone heater according to claim 4, wherein saidplurality of plate joining layers comprise metallic aluminum of greaterthan 99% by weight.
 11. The multi-zone heater according to claim 5,wherein said plurality of plate joining layers comprise metallicaluminum of greater than 99% by weight and wherein said joining layerbetween said hollow heater shaft and said multi-layer plate comprisesmetallic aluminum of greater than 99% by weight.
 12. A multi-zoneheater, said multi-zone heater comprising: a multi-layer heater plate,said multi-layer heater plate comprising: a heater plate radial center;a top plate layer, said top plate layer comprising ceramic; a bottomplate layer, said bottom plate layer comprising ceramic; a joining layerdisposed between said top plate layer and said bottom plate layer,wherein said joining layer joins said plate layers with a hermeticjoint; a plurality of heater element zones between two of the platelayers, said heater element zones adapted to be individually controlled;and a plurality of thermocouples, said thermocouples mounted betweensaid plate layers and located at a plurality of distances from saidheater plate radial center, said thermocouples comprising thermocoupleleads, wherein the hermetic joint has a vacuum leak rate of <1×10⁻⁹ sccmHe/sec and; and a ceramic hollow heater shaft, said ceramic hollowheater shaft comprising: an interior surface, said interior surface ofsaid hollow heater shaft defining an interior of said hollow heatershaft; and an exterior surface, wherein said ceramic hollow heater shaftis attached to a bottom surface of said multi-layer heater plate;wherein each of the hermetic joints have a vacuum leak rate of <1×10⁻⁹sccm He/sec and wherein said thermocouple leads are routed through theinterior of said ceramic hollow heater shaft.
 13. The multi-zone heateraccording to claim 12, wherein said joining layer comprises metallicaluminum.
 14. The multi-zone heater according to claim 13, wherein saidjoining layer comprises metallic aluminum of greater than 99% by weight.15. The multi-zone heater according to claim 13, wherein said top platerlayer comprises aluminum nitride.
 16. The multi-zone heater according toclaim 15, wherein said bottom layer comprises aluminum nitride.